1. Field of the Invention
This invention relates to flat panel display devices and, more particularly, to processes for creating fiber spacer structures which provide support against the atmospheric pressure on the flat panel display without impairing the resolution of the image.
2. State of the Art
In flat panel displays of the field emission type, an evacuated cavity is maintained between the cathode electron-emitting surface and its corresponding anode display face. Since there is a relatively high voltage differential between the cathode emitting surface and the display screen, it is important to prevent catastrophic electrical breakdown between them. At the same time, the narrow spacing between the plates is necessary for structural thinness and to obtain high image resolution. Spacer structures incorporated between the display face and the baseplate perform these functions.
In order to be effective, spacer structures must possess certain characteristics. They must have sufficient non-conductivity to prevent catastrophic electrical breakdown between the cathode array and the anode. This is necessary because of both the relatively close inter-electrode spacing (which may be on the order of 200 .mu.m), and relatively high inter-electrode voltage differential (which may be on the order of 300 or more volts).
Further, the supports must be strong enough to prevent the flat panel display from collapsing under atmospheric pressure. Stability under electron bombardment is also important, since electrons will be generated at each of the pixels. The spacers must also withstand "bake-out" temperatures of around 400.degree. C. used in forming the high vacuum between the faceplate and baseplate of the display.
For optimum screen resolution, the spacer structures must be almost perfectly aligned to array topography. They must be of sufficiently small cross-sectional area so as to be invisible during display operation. Hence, cylindrical spacers must have diameters no greater than about 50 microns. A single cylindrical lead oxide silicate glass column, having a diameter of 25 microns and a height of 200 microns, will have a buckle load of about 2.67.times.10.sup.-2 newtons. Buckle loads, of course, will decrease as height is increased with no corresponding increase in diameter.
It is also of note that a cylindrical spacer having a diameter d will have a buckle load that is only about 18% greater than that of a spacer of square cross-section and a diagonal d, although the cylindrical spacer has a cross-sectional area about 57% greater than the spacer of square cross section.
Known methods for spacer fabrication using screen-printing, stencil printing, or glass balls do not provide a spacer having a sufficiently high aspect ratio. The spacers formed by these methods either cannot support the high voltages, or interfere with the display image. Other methods which employ the etching of deposited materials suffer from slow throughput (i.e., time length of fabrication), slow etch rates, and etch mask degradation. The use of lithographically defined photoactive organic compound results in the formation of spacers, which are incompatible with the high vacuum conditions, and elevated temperatures characteristic in the manufacture of field emission displays (FED).
Accordingly, there is a need for a high aspect ratio spacer structure for use in a FED, and an efficient method of manufacturing a FED with such a spacer.